1. Field of the Invention
The present invention relates to a micropump, in particular, which is driven by continuous electrowetting actuation.
2. Description of the Related Art
Necessity of a micropump treating an ultra-small amount of liquid is being increasingly proposed in various fields such as a micro chemical analysis system, implantable medical devices, micro drug injectors, and a micro manufacturing system.
Conventional micropumps utilize piezoelectric force, electrostatic force, thermopneumatic force, electromagnetic force and the like as driving energy thereof. However, the piezoelectric or electrostatic force requires a high driving voltage of about several hundreds of volt, and the thermopneumatic or electromagnetic force consumes a large amount of electric power. Therefore, the micropumps based upon the foregoing schemes are disadvantageous to be used in the implatable medical devices, a remote environment monitoring system, the handheld chemical analysis system and the like.
U.S. Pat. No. 5,472,577 granted to Mark D. Porter et al., Dec. 5, 1995, discloses a micropump which is driven by electrically changing the surface tension of liquid metal in a vessel. In accordance with this document, the driving energy of the micropump is obtained based upon variation in radius of curvature by electrically changing the surface tension at a surface of the liquid metal contacting with electrolyte.
Accordingly, the present invention has been devised to solve the foregoing problems of the prior art and it is a technical object of the invention to provide a micropump which has an improved operational characteristic based upon a continuous electrowetting phenomenon.
It is another technical object of the invention to provide a micropump capable of operating with low power consumption and a low operating voltage.
It is further another technical object of the invention to provide a micropump capable of large deflection of membrane compared to a conventional micropump based upon variation of surface tension.
It is another technical object of the invention to provide a micropump having at least two drivers connected in series or parallel to increase pumping pressure and obtain large deflection of membrane.
It is still another technical object of the invention to provide a micropump which is readily fabricated by employing a micro-machining or semiconductor processes.
In accordance with an aspect of the invention for obtaining the foregoing technical objects, a micropump is based upon continuous electrowetting actuation, in which the surface tension of the liquid drop is electrically changed in succession to move a liquid drop. The micropump consists of a driving part containing deflectable thin membrane, a channel which guide the media to be pumped, and check valves which direct the flow of pumping fluid into one direction.
In the micropump of the invention, a driving part includes an elongated capillary tube or a micro tube filled with an electrolyte solution, a liquid drop inserted into the tube, metal electrodes for applying voltage and flexible membranes which are moved by the shoved electrolyte solution as the liquid drop moves.
In the driving part, the voltage applied to the metal electrode forces the liquid drop to move and thus the electrolyte solution, thereby deflecting the flexible membranes. As the voltage is applied to the electrolyte solution via the metal electrodes, surface tension is distributed with different intensity along the surface of the liquid drop in the tube. The difference of surface tension forces the liquid drop to move into one direction. Movement of the electrolyte solution is accompanied, and the membranes blocking both ends of the capillary tube are deflected due to a corresponding pressure.
In accordance with the invention, the driving part is proposed as a driver of the micropump to guide or control the flow of liquid or gas. The liquid drop is inserted into the center of the capillary tube or elongated tube filled with the electrolyte solution. The liquid drop is generally made of oil or liquid metal such as mercury or indium alloy. The electrodes for applying voltage are inserted into the both ends of the tube, which are flared and then blocked with the thin flexible membranes. The flexible membranes constitute an outside wall of the tube through which fluid to be pumped practically flows, and induce the flow of fluid via vertical reciprocation motion. Preferably, the polarity of applied voltage is periodically change in order to induce reciprocation motion of the liquid drop and accordingly vertical reciprocation motion of the membranes. More preferably, the applied voltage is a square wave voltage having a predetermined period and amplitude.
In accordance with another aspect of the invention, the micropump is fabricated by using semiconductor processes or micromachining. A flat substrate such as a glass substrate or silicon substrate is used to form a structure via the semiconductor processes or micromachining. The metal electrodes are formed on the substrate, and the channel in which the electrolyte solution and the liquid drop move can be made of a thick coating material such as a photosensitive film or polymer. Movement of the liquid drop is also transferred to the fluid to be pumped via the flexible membranes blocking the ends of channel.
In accordance with further another aspect of the invention, the driver further includes at least one tube which is identical with the foregoing tube into which one liquid drop is inserted. The at least one additional tube is connected with the foregoing tube in series or parallel to enhance the performance of the micropump. The pumping pressure can be increased with the serial connection of more than two drivers which contain their own liquid drops to be operated. Further, the large deflection of membrane is obtained by increasing the volume of electrolyte solution to be pushed or dragged through the parallel connection of the drives. Moreover, the drivers combine serial connection and parallel connection structures to deflect the membrane by a large amount with a large pumping pressure.